In a gas turbine installation, a gaseous or liquid fuel, for example natural gas or mineral oil, is mixed with compressed air, and is burnt. The pressurized combustion exhaust gases are supplied to the turbine of the gas turbine installation as a working medium. The working medium causes the turbine to rotate as it expands, with thermal energy being converted to mechanical work, specifically rotation of the turbine shaft. When the expanded working medium emerges from the gas turbine installation, it is typically still at a temperature of 500-600° C.
In a gas and steam turbine installation, the expanded working medium, also referred to as flue gas, from the gas turbine installation is used to generate steam for driving a steam turbine. For this purpose, the working medium is supplied to a waste-heat steam generator which follows the gas turbine installation on the exhaust gas side and in which heating surfaces are arranged in the form of tubes or tube bundles. The heating surfaces are in turn connected to a water/steam circuit of the steam turbine installation, which circuit has at least one, but generally more, pressure stage or stages.
At the moment, a gas and steam turbine installation is normally started by starting the gas turbine installation and by supplying the expanded working medium to the waste-heat steam generator of the steam turbine installation. The steam which is generated in the waste-heat steam generator is, however, not supplied first of all to the turbine part of the steam turbine installation, but bypasses it, via bypass stations on the turbine, and is supplied directly to a condenser, which condenses the steam to form water. The steam turbine is not connected until specific steam parameters are complied with in the steam lines of the water steam circuit and/or in the steam lines which lead to the turbine section of the gas turbine installation, for example specific steam pressures and temperatures. Maintenance of these steam parameters is intended to keep possible stresses in thick-walled components at a low level. Once the gas turbine installation has been started, the power rises and this leads to a pressure rise in the steam system. One governing factor for the load gradient which occurs during starting of the gas turbine installation, that is to say the power increase of the gas turbine installation per unit time, is the configuration and method of construction of the waste-heat steam generator and the design limitations within the steam turbine. As the gas turbine load, and therefore the temperature and the volume flow of the exhaust gas emitted from the gas turbine installation, rise, the steam temperature and the pressure in the steam system also increase.
The design of fossil-fuelled power station installations, for example a gas and steam turbine installation, is based inter alia on the expected load cycle. The rates of load change, for example the starting and stopping processes or else individual load cycles, are chosen during the design stage such that the theoretical component life would have been completely used at the end of the planned life of the power station installation. The actual life consumption at any given time can be indicated by life monitoring systems.
The progressive liberalization of the power markets has resulted in the demand for fossil-fuelled power station installations to be started with as fast a starting time as possible and for them to be operated on a load cycle basis, based on the same aspect assumptions, with a fossil-fuelled power station installation. On the basis of the present prior art, load changes occur in a fossil-fuelled power station in accordance with specific permissible limits, for example particularly the stress-critical components of the installation such as the boiler, steam turbine or gas turbine, which are governed by the design of their individual components. These are either calculated as rigid limits in an automation system, or are calculated at the same time by means of an optimization system. One example of this is the calculation of the optimum boiler limits for fired boilers. However, these optimization systems do not provide any information before load cycling and therefore additionally, for example, do not allow the time or the life consumption to be actively influenced as a function of the market requirements.
However, matching rates of load change to the respective actual market requirements results in the life consumption of individual components being influenced deliberately, to a major extent. This results in a requirement for the life consumption of the individual components to be as low as possible during the load cycles that are carried out. This allows the flexibility of a fossil-fuelled power station installation to be considerably increased during starting and in the event of load cycling, contributing to customer usefulness, which actually represents a competitive advantage for an installation such as this in a liberalized electricity market.
By way of example, this is disclosed for a steam turbine in EP 0 937 194 B1. With a time requirement being included, EP 0 937 194 B1 specifies a turbine control device for closed-loop control of a load cycling process in a turbine, by means of which a flexible change in the operating conditions of the turbine is achieved, which complies with the operating requirements to generate electrical power, taking account of the maximum permissible material stress. With the time duration being specified, EP 0 937 194 B1 determines a turbine control variable in the limiting unit for closed-loop control of the load cycling process, which turbine control variable is determined as a function of time in the time duration between leaving the initial state and reaching the intended state.
Furthermore, the material fatigue is determined for the load cycling process to be carried out in accordance with the turbine control variable. The additional material fatigue can therefore be calculated in advance, so that it is possible to use this material fatigue and the operating time of the turbine that is still desired manually or automatically to decide whether the load cycling process should actually be carried out in the desired time period.